1. Field of the Invention
The invention relates to an electrolyte solution that, when used in a magnesium battery, provides a larger redox current than heretofore and to a magnesium battery that contains this electrolyte solution.
2. Description of Related Art
A secondary battery is capable of discharging by converting a decline in chemical energy associated with a chemical reaction into electrical energy. A secondary battery is also capable of accumulation (charging) by converting electrical energy to chemical energy when the flow of current is reversed from that during discharge. Magnesium batteries use magnesium, which is an abundant natural resource, is easy to handle, and has a high energy density, and have been under development for a relatively long time among secondary batteries.
The reaction in equation (I) occurs at the negative electrode during discharge in the case of a magnesium battery that uses magnesium metal as its negative electrode active material.Mg→Mg2++2e−  (I)
The electrons produced according to equation (I) travel through the external circuit and perform work at an external load and subsequently reach the positive electrode. The magnesium ion (Mg2+) produced in equation (I) moves from the negative electrode side to the positive electrode side by electroosmosis within the electrolyte sandwiched between the negative electrode and positive electrode.
In addition, the reaction in equation (II) occurs at the positive electrode during discharge when vanadium pentoxide (V2O5) is used as the positive electrode active material.V2O5+Mg2++2e−→MgV2O5  (II)During charging, the reverse reactions in equations (I) and (II) occur, respectively, at the negative electrode and positive electrode, and magnesium is regenerated at the negative electrode and vanadium pentoxide (V2O5) is regenerated at the positive electrode, thus enabling discharge to occur again.
The art of a magnesium secondary battery electrolyte solution containing an ester-type electrolyte solution that incorporates a condensed phosphate is disclosed in Japanese Patent Application Publication No. 2012-150924 (JP 2012-150924 A) as art related to magnesium battery electrolyte solutions.
A solution provided by the addition of a condensed phosphate to an ester-type electrolyte solution, e.g., a propylene carbonate (PC) solution, is described as an electrolyte solution in paragraph [0020] of the Description in JP 2012-150924 A.